Lesson 10 & 11 Flashcards
preservation by ionizing energy; effect of food processing on nutrient retention
Radiation
rays of energy
emission and propagation of energy through matter or space by electromagnetic disturbances
Food irradiation
application of radiation, as ionizing energy, to foods
* using gamma rays, x-rays, or electron beam
* no significant heat produced, aka cold sterilization/pasteurization (old terminology)
i.e. process of exposing foods to radiation
Food irradiation according to Division 26 of FDA Canada
treatment of food with ionizing radiation
- gamma radiation from Cobalt-60 or Cesium-137 source
- x-rays from machine source (≤ 5 MeV)
- electron beam of beta particles from machine source (≤ 10 MeV)
MeV = megaelectron volt
beta particles = electrons accelerated to 99.9% of speed of light
Electromagnetic radiation
waves of the electromagnetic field organized on a spectrum based on their wavelength, frequency, and energy value
e.g. radio waves, microwaves, visible light, ionizing radiation
Ionizing energy
short/low wavelengths, higher frequency, and higher energy (or penetrating power)
e.g. gamma rays, x-rays
Gray (Gy)
food irradiation
amount of energy absorbed by the food treated with ionizing energy
1000 Gy = 1 kGy (kilogray); Most countries regulate 10 kGy or less of absorbed energy
2 forms of radiation pasteurization (≤ 10 kGy)
- radurization: kills majority of spoilage-causing MOs
- radicidation: kills or inhibits disease-causing MOs
Radappertization
form of radiation sterilization (> 10 kGy)
kills or inactivates all disease- and spoilage-causing MOs capable of growing at storage conditions
i.e. commercial sterilization at doses > 10 kGy (e.g. 20, 30)
not allowed in Canada!
Microwave energy
- long wavelengths, low penetrating power
- heat by intermolecular friction (causes polar molecules in food to vibrate) then conducted to neighboring molecules
- abosrbed by food up to a depth of 5-7.5 cm
core to surface!
heat passes through air, glass, paper, and plastic, but is reflected by metals (causes sparks)
Does irradiation induce radioactivity in foods?
not enough energy to penetrate the nucleus and split atoms, causing radioactivity
only enough energy to change atoms by knocking an electron from an outer orbit, forming ions and preserving food
Minimum energy required to make food radioactive
exposure to at least 15 MeV
food can never become radioactive from irradiation using the approved, carefully regulated sources (operate at max 5 or 10 MeV)
4 steps of the irradiation process
- Conveyor system moves food in boxes
- Carried into a chamber with irradiation source (e.g. Cobalt 60)
- Absorbed dose depends on the amount of time food is exposed to the irradiation source
- Dosimeters are placed with the food to measure the dose received (kGy)
Direct effect
basis for food preservation by ionizing radiation
- direct hit of ionizing energy upon genetic material of microbial cells
- can cause random, extensive damage depending on dose, MO, repair mechanism, etc.
e.g. break bonds of DNA
Indirect effects
basis for food preservation by ionizing radiation
- ionizing energy interacts with water in the food
- absorbed energy dislodges electrons from water molecules
ionizing energy > absorbed by food (water) > produces ion pairs and free radicals (reactive), which can damage key proteins, cell membrane, inhibiting MO growth
Free radicals
NOT unique to irradiated foods
also produced within our bodies and other living tissues (e.g. metabolism, oxidative reactions in foods like unsaturated fats)
mechanisms (chemical and enzymatic) within the human body inactivate free radicals
What other products are formed during food irradiation?
i.e. radiolytic products
besides ion pairs and free radicals
- benzene and derivatives, which form low concentrations after irradiation and also found in non-irradiated foods
- Alkylcyclobutaniones (ACBs) are unique radiolytic products, mostly from fatty acids
Alkylcyclobutaniones (ACBs)
unique radiolytic products
- formed via irradiation of triglycerides (fats), forming 2-ACBs (e.g. 2-DCB from palmitic acid)
- no significant health impacts at standard doses based on mutagenic/genotoxic studies
but potential for DNA damage at extremely high doses!
4 ways to minimize undesireable effects of food irradiation
free radicals
- frozen state lowers production and mobility of free radicals
- vacuum minimizes oxidative changes
- free radical scavengers (e.g. ascorbic acid) react with free radicals (have affinity)
- lowest effective irradiation dosage + effective packaging
frozen state can also reduce efficiency of preservative effect
Food irradiation at < 1 kGy
- inhibiting sprouting of vegetables
- kill insects eggs, larvae
- slow ripening
- inactivate parasites
e.g. potatoes, wheat, bananas, pork
Food irradiation at 1-10 kGy
- eliminate pathogenic bacteria (e.g. Salmonella, E. coli O157:H7) and parasites
- eliminate spoilage-causing MOs (e.g. mould)
e.g. chicken, ground beef, fruit (fresh strawberries), vegetables
Food irradiation at 10-50 kGy
commercially sterilizes food
e.g. sterilized hospital dierts, space missions foods
4 main principles of safety and wholesomeness of irradiated foods
- radiological safety: will radioacitivity be induced in food? (max 10 kGy dose)
- toxicological safety: any toxic or carcinogenic substances? (perform toxicological testing)
- microbiological safety: is the target MO killed and could MOs become more virulent? (use D10 value and perform microbiological testing)
- nutritional adequacy: significant loss of any nutrient? (perform nutrient retention testing)
Who is responsible for irradiated foods in Canada?
- HPFB of Health Canada for safety and wholesomeness of irradiated foods
- CFIA for labeling of irradiated foods and inspection of facilities
max dosage allowed is 10 kGy with all 4 main principles met and minor nutrient loss
Who is responsible for irradiated foods in the US and internationally?
- FDA in the US
- WHO internationally
D-value in irradiation
similar to concept of decimal reduction time in thermal processing
D10 value = dose (kGy) of ionizing energy needed for a 90% decrease (1 log reduction) of MO population
different doses for 5D (acid) or 12D (low-acid) process per pathogen
unlike MOs, irradiation can’t be used to inactivate enzymes (even more resistant than C. botulinum, requiring ~200 kGy), instead use blanching or other treatments
4 labelling requirements in irradiated foods
- basic info (e.g. common name, ingredient list, nutrition table, etc.)
- international radura symbol
- statement indicating product is irradiated
- identified as irradiated in ingredient list if it comprises ≥ 10% of a pre-packaged food
Foods allowed for irradiation in Canada
- potatoes and onions for sprout inhibition (0.15 kGy)
- wheat, wheat flour for infestation control (0.75 kGy)
- whole or ground spices, dehydrated seasoning preparations (10 kGy), fresh raw ground beef (4.5 kGy), frozen raw ground beef (7 kGy) to reduce microbial load
Benefits of food processing
risk-benefit analysis
- safety (destroys pathogens)
- enhanced shelf life (inactivates enzymes, destroys spoilage, reduce rate of chemical reactions)
- improved digestibility of some components
- destruction of some anti-nutritional compounds
- increased variety or enhanced palatability of some foods
e.g proteinase inhibitors, avidin, enzymes like thiaminase
Avidin
anti-nutritional compound
- a protein found in raw egg white, forming avidin-biotin complex when combined with biotin (vitamin B7)
- non-digestible or not absorbed from the intestine
deprived of B7 when we eat raw egg white
Thiaminase
anti-nutritional compound
- enzyme found in a few plants, raw flesh, and viscera of some fish and shellfish
- when ingested, splits (hydrolyzes) thiamin (vitamin B1), making it inactive,
Risks of food processing
risk-benefit analysis
- possible production of undesireable (sensory) or potentially toxic (at high doses) new compounds (e.g. ACBs)
- decreased nutrient value
3 factors affecting the extent of nutrient loss due to processing
- type of nutrient: some are more stable than others (e.g. minerals compared to vitamins)
- properties of food: stability may vary with pH and heat transfer rate
- processing methods and conditions
- storage: environmental conditions (e.g. oxygen, light, heat, moisutre) and type of packaging
- minerals only vulnerable to physical loss (e.g. leaching, milling)!
- heat transfer is slower in solid (conduction) than liquid (convection) products
Effect of processing on proteins and carbs
losses in digestibility/bioavailability usually only after severe treatments with extreme pH (low-acid)
bioavailability = how efficiently body digests, absorbs, utilizes
Effects of processing on fats
prone to hydrolytic and oxidative reactions
* prolonged storage in presence of O2
* excessively high temp or pH
* enzymatic action (e.g. lipases)
* irradiation in presence of O2
little change after moderate processes!
Stability of vitamins according to pH
- high acid foods undergo less severe thermal processes = less nutrient loss
- vitamin A unstable at pH 7
- vitamin C unstable at pH ≥ 7
- vitamin E remains stable at broad range of pH
Effect of processing methods and conditions on nutrient loss
for thermal processing, depends on:
* severity of the process (e.g. blanching vs canning)
* method (e.g. microwave, canning, cooking in water vs steam, bake)
cooking in water = leaching
for irradiation, thiamin (vitamin B1) is most vulnerable
3 ways to accomplish nutrient addition
- restoration (replacement)
- fortification (addition of not previously present)
- enrichment (mandatory fortification) to achieve specific levels requested by regulation
regulatory decisions on which foods may be approved for nutrient addition, and whether optional or mandatory
